<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var first_input = prompt("请您输入第一个值");
        var second_input = prompt("请您输入第二个值");
        var add = parseFloat(first_input) + parseFloat(second_input);
        alert('您的结果是' + add);
    </script>
</body>

</html>